In episerver I have 6 forms and each form points to its own list in marketo (solution, product, services, support, event, download).

I created and assigned the respective list to its form to create some separation of concern between the leads coming in to marketo from the site.

I can't see how to get a lead to exist in more than one lead list at any given time. I was under the impression that these were almost like playlists in itunes, where the lead is aliased in a lead list.

There is no reason why a user might want to use anyone of these forms, during a browsing session.

A new lead is added to the correct lead list, but subsequent form submissions by that lead to another form don't add that lead to the correct lead list.

Checking a lead activity log, added to list is only registered when a new lead is created.